ARTIFICIAL STONE, OR CONCRETE 



come clean when embedded in concrete, but that it be- 

 comes more effectively protected against oxidation 

 than clean iron which has been similarly treated. A 

 rusty nail and a clean nail were both embedded 

 in the same concrete block and left for over three 

 years; on being taken out the rusted nail had become 

 free from rust. Both nails, together with a new nail, 

 were then placed in water; the new nail rapidly be- 

 came rusted. The nail which was rusty when first 

 embedded in the concrete block showed no signs of 

 rust a month after being placed in the water, except 

 at one place, where it had been scraped with a pen- 

 knife before being immersed ; the other nail, after re- 

 sisting the action of the water for a few days, showed 

 signs of rusting, which increased with time." 



Very early in the history of the development of re- 

 inforced concrete experimenters considered the possi- 

 bility of utilizing this material in place of iron for the 

 drainage pipes and water-supply systems of buildings. 

 Ordinary concrete, made with a high percentage of 

 the coarser materials, such as gravel or broken rock, 

 does not resist penetration by water under high pressure 

 sufficiently for this purpose. But by using a higher 

 percentage of cement and fine sand, the concrete 

 becomes sufficiently resistant to penetration for all 

 ordinary purposes; and by adding a little soft soap 

 and alum to such concrete it can be made abso- 

 lutely impermeable without affecting its strength. 

 The proportions used for this purpose are about two 

 pounds of soap and twelve pounds of alum to every 

 cubic yard of concrete mortar. This may be used as 



